The present invention relates to a vehicle seat belt retractor which has a tension reducing mechanism for increasing the comfort of a vehicle occupant wearing seat belt webbing which is associated with the seat belt retractor.
A known seat belt retractor has two springs for biasing a seat belt webbing storage spool to rotate in a seat belt webbing retraction direction relative to a retractor frame. The two springs are connected in series with a ratchet wheel interposed between the two springs. One end of the first spring is fixed relative to the retractor frame and the other end is attached to act on the ratchet wheel. One end of the second spring is attached to the ratchet wheel and the other end is attached to act on the spool. Upon withdrawal of stored seat belt webbing from the spool, the first and second springs are stressed and the ratchet wheel is rotated in a seat belt webbing withdrawal direction.
The retractor has a comfort mechanism which is actuatable to block rotation of the ratchet wheel relative to the frame in the seat belt webbing retraction direction. Thus, when the comfort mechanism is actuated, only the spring force of the second spring is applied to bias the spool. This is a comfort setting in which a reduced tension is placed upon the seat belt webbing. Thus, the seat belt webbing applies a reduced tension to the vehicle occupant. The reduced tension increases the comfort of the vehicle occupant.
The first spring has a stronger spring force than the second spring. When the comfort setting is released and the ratchet wheel is permitted to rotate in the retraction direction, the first spring drives the ratchet wheel. The rotating ratchet wheel winds the second spring as a result of the larger spring force of the first spring being applied to the weaker second spring. If sufficient stress is present in the first spring, the second spring may be wound solid. Repeated impact of the force of the first spring on the second spring may cause unnecessary stress in the second spring.